import math

px, py, qx, qy = map(float,input().split())
pq = (qx - px) ** 2 + (qy - py) ** 2

print(math.sqrt(pq))

 import math math px, py, qx, qy = map(float,input().split()) px map(float,input().split()) map float input().split() ().split () input split py qx qy pq = (qx - px) ** 2 + (qy - py) ** 2 pq (qx - px) ** 2 + (qy - py) ** 2 (qx - px) ** 2 qx - px qx px 2 (qy - py) ** 2 qy - py qy py 2 print(math.sqrt(pq)) print math.sqrt(pq) math.sqrt math sqrt pq pq = (qx - px) ** 2 + (qy - py) ** 2 (qx - px) ** 2 + (qy - py) ** 2 pq qx, qy = map(float,input().split()) map(float,input().split()) qx px, py, qx, qy = map(float,input().split()) map(float,input().split()) px py, qx, qy = map(float,input().split()) map(float,input().split()) py qy = map(float,input().split()) map(float,input().split()) qy
import math

px, py, qx, qy = map(float,input().split())
pq = (qx - px) ** 2 + (qy - py) ** 2

print(math.sqrt(pq))


